Quote:A revolutionary UK spaceplane concept has been boosted by the conclusions of an important technical review.

The proposed Skylon vehicle would do the job of a big rocket but operate like an airliner, taking off and landing at a conventional runway.

The European Space Agency's propulsion experts have assessed the details of the concept and found no showstoppers.

They want the next phase of development to include a ground demonstration of its key innovation - its Sabre engine.

This power unit is designed to breathe oxygen from the air in the early phases of flight - just like jet engines - before switching to full rocket mode as the Skylon vehicle climbs out of the atmosphere.

It is the spaceplane's "single-stage-to-orbit" operation and its re-usability that makes Skylon such an enticing prospect and one that could substantially reduce the cost of space activity, say its proponents.

Mature concept
The UK Space Agency (UKSA) had commissioned Esa to evaluate the design, and the European organisation's staff reported on Tuesday that they had not seen any obvious flaws.

"Esa has not identified any critical topics that would prevent a successful development of the engine," they write in their review.

Skylon has been in development in the UK in various guises for nearly 30 years.

It is an evolution of an idea first pursued by British Aerospace and Rolls Royce in the 1980s.

That concept, known as Hotol, did have technical weaknesses that eventually led the aerospace companies to end their involvement.

But the engineers behind the project continued to refine their thinking and they are now working independently on a much-updated vehicle in a company called Reaction Engines Limited (REL).

Realising the Sabre propulsion system is essential to the success of the project.

The engine would burn hydrogen and oxygen to provide thrust - but in the lower atmosphere this oxygen would be taken directly from the air.

This means the 84m-long spaceplane can fly lighter from the outset with a higher thrust-to-weight ratio, enabling it to make a single leap to orbit, rather than using and dumping propellant stages on the ascent - as is the case with current expendable rockets.